1. Field of the Invention:
The present invention relates to a microscopic digital photography system. In particular, the present invention relates to a microscopic digital photography system comprising a microscope and an image pickup device for photographing an image of a sample observed by using the microscope and making conversion into an electric signal.
2. Description of Related Art:
A microscopic digital photography system has been hitherto known for photographing and recording an image of a sample observed by using a microscope. In this system, a reflecting member is arranged on an optical axis (optical axis of an objective lens and an imaging lens) of the microscope. The reflecting member is used to divide the optical path into those concerning an observing optical system and an image pickup optical system. A magnified image of the sample, which is formed on an image plane on the side of the observing optical system, is observed through an eyepiece lens. The light flux of the sample image, which is focused on the image plane on the side of the image pickup optical system, is photographed by an image pickup device arranged on the image plane. An obtained image is converted into an electric signal.
The method for dividing the optical path into those concerning the observing optical system and the image pickup optical system includes several systems. FIGS. 4 and 5 show representative systems with optical paths.
FIG. 4 shows a system in which a half prism 102 is arranged on an optical axis 104 of a microscope between an objective lens 106 and an imaging lens 108B. In this system, the optical path, through which the light flux (light flux of an image of a sample 110) coming from the objective lens 106 is transmitted by the aid of the half prism 102, is utilized as an observing optical path. In this observing optical path, the light flux is focused in the vicinity of a front focal plane of the eyepiece lens 114 through the imaging lens 108B and a view prism 118 to observe an image 112. On the other hand, a second imaging lens 108D is arranged on an optical path for the light flux which comes from the objective lens 106 and which is reflected by the half prism 102. An image pickup device 116 is arranged on an image formation plane of the second imaging lens 108D. Thus, the image pickup optical path is constructed. This system is used for an intermediate body tube type beam splitter in which a beam splitter is arranged in an intermediate body tube in a microscope of the type capable of installing an intermediate body tube unit between a main microscope body and an observing body tube. The system is constructed by arranging a digital still camera containing an image pickup device, at an output section of an optical path divided by the beam splitter to obtain a magnified image of a sample. Another intermediate body tube is also known, in which an image pickup device is contained in a housing.
FIG. 5 shows a system in which a view prism 120 is arranged over an imaging lens 122 on an optical axis of a microscope. In this system, a magnified image 124 of a sample is observed, which is formed in the vicinity of a front focal plane 124 of an eyepiece lens 126 disposed on a side of an optical path for a light flux (light flux of the image of the sample 110) which comes from an objective lens 106 and which is reflected by the view prism 120. An image pickup device 116 is arranged on an image plane on a light path for a light flux transmitted through the view prism 120. A magnified image, which is formed on the image plane, is photographed. This system is adopted in many microscopes having a trifurcate body tube provided with a binocular unit for observation and a straight barrel for photographing operation. Such a system is constructed by attaching, to the straight barrel, a digital still camera containing an image pickup device. Another body tube is also used, in which an image pickup device is contained in a housing. In the system constructed as described above, a photographer operates a focusing handle of the microscope while looking into the binocular unit of the body tube so that the focal point is adjusted to the sample.
Besides, a system is also known, in which a digital still camera of the single-lens reflex camera type is used. In this case, the focusing operation is performed for the microscope by making observation through an optical finder of the digital still camera. In other cases, the digital still camera is connected to a computer. A real time image, which is captured by an image pickup device, is displayed on a monitor of the computer. The focusing operation is performed for the microscope while observing of the image.
However, the microscopic digital photography system, which adopts the system shown in FIGS. 4 and 5 described above, has an inconvenience in that it is impossible to confirm the range of the image projected onto the picture element of the image pickup device during the photographing operation.
When the photographer performs the focusing operation for the microscope while looking into the binocular unit of the body tube so that the focal point is adjusted on a sample, the resolving power for the image, which is obtained by looking into the binocular unit by the photographer, is generally different from the resolving power possessed by the image photographed by the image pickup device of the digital still camera. The resolving power, which is obtained by viewing a photographing range with human eyes, is converted into the number of picture elements of the image pickup device as follows:
((photographing length in longitudinal direction/resolving power of naked eye).times.2).times.((photographing length in transverse direction/resolving power of naked eye).times.2). PA1 a microscope having an objective lens and an eyepiece lens; PA1 an image pickup device for photographing an image of the sample formed by the objective lens; PA1 a display unit having a screen for displaying the image; PA1 a controller for controlling the display unit so that the image is displayed on the screen of the display unit on the basis of a signal outputted from the image pickup device; and PA1 a first optical system for guiding a light flux from the screen to the eyepiece lens. PA1 a microscope having an objective lens, an eyepiece lens, and a housing for accommodating them; PA1 an image pickup device accommodated in the housing, for photographing an image of a sample formed by the objective lens; PA1 a screen accommodated in the housing, for displaying the image photographed by the image pickup device; and PA1 a displaying optical system accommodated in the housing, for guiding a light flux from the screen to the eyepiece lens. In this system, not only the image pickup device but also the display unit are contained in the housing or a body tube of the microscope. It is possible for the photographer to observe, through the eyepiece lens, the image projected on the screen, in the same manner as in the system according to the first aspect. Therefore, the system of the present invention can enjoy the merit that the image of the sample photographed by the image pickup device can be previously observed through the screen, while having the size or the installation area approximately equivalent to those for the conventional system. The system of the present invention may further comprise a controller for displaying the image on the screen on the basis of a signal outputted from the image pickup device.
It is now assumed, for example, that the field number of a 10.times.eyepiece lens is 20 mm, and the photographing range is 12 mm.times.16 mm (diagonal: 20 mm) inscribing the size of the observing field. The resolving power of the human eye is generally 0.14 mm at the distance of distinct vision (250 mm). Therefore, the resolving power is 0.014 mm on the image plane when a sample is viewed through the 10.times.eyepiece lens. In order to obtain a resolving power approximately equivalent to the resolving power of the human eye, the following number of picture elements is required: EQU ((12/0.014).times.2).times.((16/0.014).times.2)=3918367.
That is, it is necessary to use a number of picture elements of about four millions.
However, the digital still camera, which is provided with an image pickup device having a number of picture elements of four millions, is used for commercial digital photographs, but it is not generally used. Therefore, such an instrument tends to be extremely expensive. In general, a digital still cameral having a number of picture elements of about three hundred thousand is utilized. Therefore, when the entire observing field is photographed by using the general digital still cameral having the number of picture elements of about three hundred thousand, the resolving power of the photographed image is extremely coarse as compared with the image captured by the naked eye observation. As a result, it is impossible to obtain an image expected by the photographer.
Therefore, even when the digital still camera having a small number of picture elements is used, the photographing operation is preferably performed by magnifying and projecting a narrow range of a sample onto the image pickup device plane, not by projecting the entire observing field onto the plane, so as to make it possible to improve the resolving power converted into one concerning the sample dimension corresponding to one picture element, i.e., the dimension of the sample. However, if a sample is magnified and photographed, the photographing range for the sample becomes narrow. Therefore, the photographer is forced to perform the operation such that a test shot is taken in order to obtain a desired image, and the photographing magnification is changed while estimating the photographed image to make a balance between a necessary size of the photographing range and necessary fineness of the image. For this reason, there has been an inconvenience that the photographing operation requires a lot of time and labor.
A similar inconvenience has also occurred when the focusing operation is performed for the microscope through an optical finder by using a digital still camera of the single-lens reflex camera type.
On the other hand, in the case of the system comprising the digital still camera connected to the computer, the real time image captured by the image pickup device of the camera is displayed on the monitor of the computer. It is possible to set the photographing range and perform the focusing operation while observing the displayed image. In this case, the image captured by the image pickup device can be confirmed on the monitor screen. However, in this case, it is necessary to install the monitor together with the computer disposed adjacent to the microscope. Therefore, an inconvenience arises in that the occupied area is increased on the desk.
In recent years, a small size personal computer, which requires a small area for installation, is generally used. Therefore, the required installation area is not so large when such a small size personal computer is used. However, the display section is small for the display screen and for a separately placed small size monitor. Therefore, the displayed image is difficult to be seen. Such a display is not suitable to confirm the resolving power for the photographed image. On the other hand, an instrument of the Braun tube type, which has a large display screen, requires an extremely large installation area. A thin type instrument, which is based on the use of a liquid crystal or the like, is also available. However, those having a large display screen are expensive. In addition, in the case of the system comprising the digital still camera connected to the computer, it is necessary to perform the focusing operation while viewing the display screen placed outside of the microscope. Therefore, such a system is different in way of use from an ordinary microscope, causing an inconvenience that such a system feels difficult to be used.